*{box-sizing: border-box}
#buttons{
    position: fixed;
    right: 0;
    top: 0;
    z-index: 10;
    display: flex;
    flex-direction: column;
    margin-top: 10px;
    margin-bottom: 10px;
}
#buttons > button{
    margin-bottom: 10px;
    padding: 4px 8px;
}
#demo{
    position: fixed;
    height: 50vh;
    top: 0;
    left: 0;
    width: 100%;
    overflow-y:auto;
}
#demo::-webkit-scrollbar{
    display: none;
}
#html{
    position: fixed;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 50vh;
}